Xu “Sirius” Li, PhD, an assistant professor and plant metabolic pathway engineer with the NC State University Plants for Human Health Institute (PHHI), uses the model plant system Arabidopsis to understand how plants produce secondary metabolites and support human health. In collaboration with other scientists at PHHI and at the NC Research Campus, he is applying that knowledge to real-world needs.

Flavonoids are one of the most abundant secondary metabolites in plants. Secondary metabolites are the collection of chemicals inside plants that protect them and when consumed by humans have health benefits. For example, flavonoids in plants produce yellow, red and blue pigmentation; help defend against microbes, fungi and insects; are involved with ultra-violet light filtration; serve as chemical messengers; and perform other physiological functions. For humans, the consumption of flavonoids in fruits, vegetables, teas and wines are shown in research studies to have anti-inflammatory, antioxidant, antimicrobial and even anti-cancer health effects.

The challenge for scientists is two-fold. First, continuing to expand the understanding of how plants produce secondary metabolites and support human health; second, applying the knowledge to real-world needs. Xu “Sirius” Li, PhD, (pictured left) is one scientist who has taken on both sides of the challenge using the plant model system Arabidopsis.

Expanded Understanding

Li, who is an assistant professor and plant metabolic pathway engineer with the NC State University Plants for Human Health Institute (PHHI) at the NC Research Campus in Kannapolis, specifically researches the phenylpropanoid pathway, which is responsible for the biosynthesis of a variety of compounds including flavonoids.

“The idea is to look for associations between metabolite variation and genetic variation across individual plants to figure out what genes control what metabolites,” Li related. “The whole genome sequence for a large collection of Arabidopsis accessions are available, so all we need to do is metabolite profiling and association analysis.”

Linking genes and metabolites is a crucial step in knowing how plants make specific compounds. “Once we identified a metabolite-gene association, we will need to validate it,” Li stated. “Arabidopsis is an ideal platform to do that. Such validation is often not feasible or takes a long time to do in crops. With Arabidopsis, in a few months, you know the answer.”

Real-World Applications

Li and PHHI’s Tzung-Fu Hsieh, PhD, a systems biologist and epigenesist, are just beginning to collaborate on research using Arabidopsis. Hsieh studies the development of the endosperm in plants like grains and the process of DNA methylation that directs the division and differentiation of cells. By working with Li, Hsieh is using Arabidopsis to broaden the understanding of biochemical pathways in crop plants that have limited genetic resources available.

“Certain pathways in plants only activate under very specific environmental conditions or at certain developmental stages,” Hsieh said. “There are compounds that may be beneficial to human health. By using epigenetic inhibitors in Arabidopsis, we can find out how to turn certain pathways on and off and identify compounds more easily, then translate that knowledge into other plant species.”

Li leads the broccoli research team that is part of the Plant Pathways Elucidation Project (P2EP), an academic and industry consortium exploring plant pathways and their benefit to human health. Broccoli is one of four crops currently targeted by P2EP.

“Arabidopsis is in the same family as broccoli,” Li said. “We’ve known a great number of genes and pathways in Arabidopsis. This knowledge makes elucidation of similar pathways in broccoli much easier.”

“The pathways in Arabidopsis should be simplified versions of the pathways in broccoli or Brussels sprouts, which are health protective crops,” added Mary Ann Lila, PhD, PHHI director. “So if Li can find out simple mechanisms in Arabidopsis, we can translate that to economically important health crops, especially with all we know about genomics now.”

Arabidopsis Advances Biofuels

Li has a line of research applicable to the biofuels industry.Lignin, a major component of plant cell walls, is a product of the phenylpropanoid pathway, which Li studies. Lignin impedes the cellulosic biomass to biofuels conversion. An obvious solution is to develop plants with less lignin, but those plants have a problem.

“One common thing people found is when you reduce the lignin content, you do see the increase of the cell wall degradability, (but) then the plants are usually dwarfed,” said Li. “Then you lose biomass and that makes it useless for real-world applications.”